The primary component of mucus is higher molecular weight mucin glycoproteins, which form numerous covalent and noncovalent bonds with other mucin molecules and various constituents, including DNA, alginate, and hyaluronan. Hanes et al., Gene therapy in the lung. in Pharmaceutical Inhalation Aerosol Technology, 2d ed.; Marcel Dekker Inc.: New York, 2003; pp. 489-539. Reconstituted mucus formulated from pig gastric, human cervical, and tracheobronchial mucins display similar mucus structures, with large rod or fiberlike aggregates of 5 nm in diameter and 100-5000 nm in length. Khanvilkar et al., Adv. Drug Deliv. Rev. 2001 48, 173-193. The condensed and complex microstructure of the mucus network gives rise to a highly viscoelastic gel, which significantly impedes the transport rates of large macromolecules and nanoparticles. Saltzman et al., Biophys. J. 1994, 66, 508-515; Sanders et al., Am. J. Respir. Crit. Care Med. 2002, 162, 1905-1911; Olmsted et al., Biophys. J. 2001 81, 1930-1937. Immobilized nanoparticles are subject to bacterial and enzymatic degradation and may also be cleared from the body by normal mucus clearance mechanisms. Although clearance rates are anatomically determined, mucus turnover rates in the GI tract are estimated as between 24 and 48 h. Khanvilkar et al., supra. In the lungs, clearance rates are dependent on the region of particle deposition; however, normal tracheal mucus velocities, albeit more rapid than mucus velocities in the peripheral lung, range from 1-10 mm/min and turnover times are less than 1 h. Cone, R. A. Mucus. In Mucosal Immunology, 2nd ed.; Academic Press: San Diego, Calif., 1999; pp. 43064. As a result, it is desirable to have drug and gene carriers, which are capable of efficiently traversing mucus layers coating mucosal surfaces.